# An ice-skater starts her pirouette with arms outstretched, rotating at 1.9 rev/s. Estimate her rotational speed (in revolutions per second) when she brings her arms flat against her body. (We assume that her body mass (not including her arms) is 50 kg and that each arm has a mass of 4.0 kg. Let's also assume that her arms are 1.0 m long and that her body is cylindrical with a radius of 20 cm.)

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An ice-skater starts her pirouette with arms outstretched, rotating at 1.9 rev/s. Estimate her rotational speed (in revolutions per second) when she brings her arms flat against her body. (We assume that her body mass (not including her arms) is 50 kg and that each arm has a mass of 4.0 kg. Let's also assume that her arms are 1.0 m long and that her body is cylindrical with a radius of 20 cm.)

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Step 1

The net torque acting on the ice skater is constant, hence angular momentum is constant

Step 2

Now,

Step 3

And,

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